The present invention relates to blow molding of blow molded containers, and more particularly to multiple compartment containers such as bottles and the like, multi-compartmented products such as multi-celled batteries, and multi-component products such as cosmetics and certain foods, in powders, creams, solids, or liquids.
Plastic molding is done in a variety of ways. For example in straight injection molding, a mold cavity is completely filled with a molten thermoplastic material at high pressure via one or more sprue openings of the cavity. Once the material has solidified, the mold is opened and the molded part is ejected. Some draft for the mold is generally required, and necked cavities are normally prohibited in this process, because of a need for a "contractible" male mold portion. A multiple cavity mold that does not require significant draft, however, is disclosed in U.S. Pat. No. 3,673,302 to Halsall et al.
Necked containers are commonly produced in a variety of "blow-molding" processes, wherein a layer of semi-molten plastic is formed against the walls of a female mold cavity by differential gas pressure. In such processes, a hollow plastic tube or parison is positioned within the cavity in a high temperature condition, then expanded against the cavity, usually by compressed air. As compared with straight injection molding, blow molding of bottles and other containers is considerably less expensive, primarily because of the absence of a male mold portion, and because lower molding pressures and temperatures are required.
As used herein, the term "blow molding" is meant in its generic sense, including but not limited to vacuum forming, vacuum blow molding (including air-assist), centrifugal or rotational molding, stretch-blow molding wherein the parison is axially stretched by mechanical means prior to final forming, injection blow molding wherein the parison is injection molded prior to its being positioned within the cavity, and extrusion blow molding wherein the parison is formed by an extruder die as it is being introduced into the cavity.
Multiple compartment necked containers can be produced by joining separate containers to form a unitized package, such as is described in U.S. Pat. No. 4,196,808 to Pardo. U.S. Pat. Nos. D214,549 to Ledewitz, D192,980 to Mangini et al., and D280,599 to Green each show necked multiple compartment containers that are integrally molded. A problem with such containers is that the mold itself does not define the shape of an interior wall between the compartments. Instead, the interior wall is formed by joinder of expanding bubble portions of the plastic material that are formed in mold cavity portions that define the exterior shapes of adjoining compartments of the container. The effects of gravity and/or a slight pressure differential between the compartments during molding can produce an unwanted wall contour or complete failure of the interior wall. Thus the interior wall is typically made quite narrow by the use of inward mold projections that form slots or depressions on opposite sides of the container in line with the interior wall. A disadvantage of this method for forming multiple compartment containers is that it is often desired that the exterior of the container be free of such slots or depressions.
Another problem with such integrally formed containers is that the mold cycle time is made longer to the extent that inwardly extending mold projections or blades for forming the slots require longer cooling times. Also, the interior wall, not being in contact with the mold, is not cooled thereby. Thus the interior wall is subject to deformation even after the exterior walls have substantially solidified, especially upon ejection of the part from the mold and transport thereof. A further problem, especially when the depth of opposing depressions approaches the width of the container, is that the container is weakened such that it can flex, the region between the slots acting as a hinge. Moreover, the slots collect contamination and are difficult to clean.
Multiple compartment containers are commonly used in the production of multi-celled batteries, such as in the automotive industry. The cells are in separate compartments, which must be sealed from each other. In conventional construction, a case of the battery is injection molded with partitions for defining the compartments, the partitions extending to flush with outside walls of the case. Interconnections between the cells are made by a system of angle plates and bolts that sealingly protrude the partitions. These interconnections are complicated and awkward to assemble. Also, a cover for the case must be sealingly connected along each of the partitions as well as along the outside walls of the case. It is difficult to reliably obtain such sealed connections. Moreover, detection of flawed seals is cumbersome and expensive, and repair in such instances is at best only marginally practical.
Thus there is a need for a multiple compartment container that can be inexpensively molded without the above disadvantages.